To obtain effective reverse bias characteristics of a p-n junction it is known that edge or surface leakage of carriers through or across the material surrounding the periphery of the junction needs to be minimized. In a discrete device or integrated circuit the structural element serving this function is often termed a "guard ring." In planar devices the oxide layer covering the substrate minimizes surface leakage around the junction. Other structures designed for this purpose are mesas, p-n junction guard rings, and oxide regions penetrating below the surface of the semiconductor.